Is sleep training safe and at what age?

What the evidence says

Babies don't develop a regular day-night sleep pattern until around 4 months old, so most expert sources suggest waiting until at least that age before starting any sleep training. A commonly cited sweet spot is 4 to 6 months, though some approaches can be used anywhere from 3 months to a year depending on the child and family, and it's wise to check with your pediatrician first, especially if starting early.

On safety: a randomized controlled trial comparing graduated extinction (checking in at increasing intervals) and bedtime fading against a sleep-education-only control found both approaches helped babies fall asleep faster and reduced maternal stress, with only small changes in infant cortisol. A five-year follow-up of a similar trial found no evidence of lasting harm to children's emotional or behavioral outcomes, their relationship with their parents, or maternal mental health.

That said, some researchers have pushed back on how confidently these studies can rule out harm, since cortisol data was only available for less than half of participants in the long-term follow-up, and the original graduated-extinction trial had a small sample size (43 infants). So while current evidence leans toward 'safe,' it isn't a slam-dunk certainty for every method or every child.

Whatever age you start, standard safe-sleep rules still apply until your baby turns 1: always place them on their back, alone, in a crib or bassinet with no loose bedding, ideally room-sharing without bed-sharing.